The present invention relates to a magnetic head used for magnetic reading/writing.
At present, the main emphasis in a magnetic head used for a magnetic reading device, particularly, for a flopy disc drive device is a writing and reading magnetic head in which reading and writing are carried out by a single magnetic head, in view of production cost and advantageousness of the device into simplification.
However, the writing and reading magnetic head has a disadvantage that the specific characteristics thereof are inferior to that of an exclusive-use magnetic head for the following reasons.
It is known that in writing, a magnetic field in excess of an antimagnetic force Hc of the medium need be generated in the writing medium. To this end, it is required that the length of head gap be made greater than the sum of a thickness of a writing layer of the medium and a gap between the magnetic head and the medium, that is, a spacing, so as to generate a large magnetic flux in the gap surface.
With regard to a head material, it is important that a saturated magnetic flux density of the material be large.
On the other hand, in reading, it is necessary to introduce a change in magnetization recorded in the medium to a coil portion of the magnetic head with high resolution. Therefore, it is important that the effective length of head gap in reading be narrow and that as for the material's specific characteristics, large initial permeability is needed since a fine magnetic flux being detected. For example, if the length of the head gap is greater than the writing wavelength, the change in magnetization cannot be detected. Generally, the effective length of gap is set at a value less than 1/2 of the writing wavelength.
It is not important so much that in reading, the magnetic flux density of material is large.
As described above, writing and reading magnetic heads have to be provided with special characteristics different from each other. In case of the writing magnetic head, the the length of the gap is preferably large from the viewpoint of writing efficiency, and in case of the reading magnetic head, the gap is preferably small from the viewpoint of the reading frequency characteristic. However, the length of the gap of a conventional writing and reading magnetic head is set at an approximately middle valve between the length of the gap of the read exclusive magnetic head and the length of the gap of the write exclusive magnetic head, and therefore, involves a disadvantage that the special characteristic thereof is inferior to the case which uses each exclusive-use heads for writing and reading.
On the other hand, ferrite is used as the material for the magnetic head of this kind since ferrite is excellent in accuracy of finishing, frequency characteristic, wear resistance, etc. Recently, the antimagnetic force of the medium has tended to increase due to the requirement of high density of magnetic writing, and it is difficult to provide sufficient magnetization with a saturated magnetic flux density (hereinafter referred to as "Bs") of the ferrite which is the main current of a head material.
Therefore, in a conventional writing and reading magnetic head, in setting the length of the gap, the middle value is employed with respect to the requirement contrary to writing and reading (wide in case of writing, and narrow in case of reading due to the frequency characteristics) as described above. Therefore, it is inferior in read/write characteristics such as output level, frequency characteristic or the like to an exclusive-use magnetic head for writing and reading, respectively.